1. Field of the Invention
The present invention relates to an optical switch for use in fiber communication and optical network technology, and particularly to a mechanically operated optical switch with a GRIN (graded index) lens and at least one mirror as a switching element.
2. Description of Related Art
Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optical fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals.
In optical fiber systems, various methods have been previously developed for switching optical signals between fiber cables. Among these previously developed methods, one important category is mechanical optical switches.
Mechanically operated optical switches come in two different designs: in one design, the optical components move, and in the other design, the fibers move. Factors for assessing the capability of an optical switch include low insertion loss ( less than 1 dB), good isolation performance ( greater than 50 dB) and bandwidth capacity compatible with the fiber network the switch is supporting.
Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a light beam from one fiber end to another under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses which expand the light beam coming from the fibers, and then, using moving prisms or mirrors, redirect the expanded light beam to other fibers, as required by the switching process.
The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small fraction of the fiber core diameter for two fibers to precisely collimate to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes the fibers less flexible, increasing the force required to manipulate each fiber into alignment. Thus these moving fiber switches share a common problem of requiring high precision parts to obtain precise position control and low insertion loss. This results in high cost and complicated manufacture of the switches. Moreover, frequently moving fibers to and from is apt to damage or even break the fibers.
The moving optical component switches, in contrast, have less stringent movement control tolerance requirements. The presence of the collimating lenses allows relaxation of the tolerance requirements.
As illustrated in FIG. 14 and FIG. 15, U.S. Pat. No. 5,742,712 describes a mechanical optical switch, which relies on a mirror 420 being moveable into an optical path between a first and second fixed collimating lenses (428, 436). When the moveable mirror 420 is displaced out of the optical path (FIG. 14), the light signals from a first input fiber 422 are transmitted to a second output fiber 432 and the light signals from a second input fiber 430 are transmitted to a first output fiber 424 through the first and second collimating lenses (428, 436). However, when the moveable mirror 420 is moved into the optical path (FIG. 15), the light signals from the first input fiber 422 are reflected back through the first collimating lens 428 into the first output fiber 424, which is parallel to and in close proximity with the first input fiber 422. The light signals from the second input fiber 430 are likewise reflected back through the second collimating lens 436 into the second output fiber 432, which is parallel to and in close proximity with the second input fiber 430.
In this mechanical optical switch, the gap between the two collimating lenses (428, 436), must be sufficiently large to allow movement of the movable mirror 420 between the two collimating lenses. However, this gap has a significant effect on insertion losses across the switch. For this reason, the gap is preferably less than about 2.0 mm. In addition, in a fixed collimator system initially without a mirror, the insertion of a two-surface mirror will introduce an insertion loss in an input/output port proportional to a thickness of the two-surface mirror.
For the above reasons, an improved optical switch is desired. In particularly, an optical switch is desired which has high optical efficiency and which does not require precise alignment or movement of the optical fibers themselves.
An object of the present invention is to provide an optical switch in which the optical fibers don""t move.
Another object of the present invention is to provide an optical switch which allows easy alignment of associated fibers and which has a low insertion loss.
Yet another object of the present invention is to provide an optical switch which uses a GRIN lens as a switching element.
An optical switch in accordance with one embodiment of the present invention comprises a housing, a driver, a first I/O (input/output) port, a second I/O port and a switching element. The housing holds the first I/O port and the second I/O port in alignment with one another and supports the driver on the housing substrate. The switching element is rotationally attached to the driver and has a first and second mirrors and a rod lens. The driver drives the switching element between a first position, wherein the rod lens aligns with the I/O ports, and a second position, wherein the mirrors align with the I/O ports.